Talk:Gene

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Contents 1 Gene exactly? 2 Overhaul table of gene number and genome size? 3 kudos 4 Request for references 5 Sentence moved here from article. 6 new models of evolution and genes - call for experts out there to address an issue 7 Cistron currently redirects here ... 8 Typical numbers of genes in an organism: Differentiate for plants 9 Human genome is Science Collaboration of the Week 10 WP:FARC 11 What are Thrifty Genes? 12 Modifier gene 13 0.5 version nomination 14 Usually? 15 embryology 16 Organization of this article 17 Effluvia 18 Referencing elementary material 19 Lead section comments 20 old table 21 Trichomonas vaginalis 22 Lead Problem

[edit] Gene exactly?

The article states that "in molecular biology, a gene encodes the chemical structure of a protein". Is that one and only one protein or peptide per gene? Is a gene the amino acid code between and including start codon AUG, GUG and stop codon UAG, UGA, UAA?

Thanks - Jerryseinfeld 08:16, 2 Oct 2004 (UTC)

In eukaryotes, the matter is far more complicated. There's alternative splicing, in which the RNA transcript can be modified post-transcriptionally into any of several different mRNAs. The issue of what a eukaryotic gene is is also somewhat more complicated as a result. Prokaryotes don't do splicing, as a general rule, so they're pretty much one-gene-one-protein beasties. Also, the regulatory sequences in noncoding regions around a gene are often very important to its function, so they might be included in the definition of a gene. Bryan 18:44, 2 Oct 2004 (UTC)

• "genes" were for a long time theoretical entities. Chromosomes can be observed under a light microscope, so they seem to qualify as "physical entities". Molecules (including DNA), once theoretic entities, now would seem to be indirectly observable via electron-microscopes. In the scheme of things, genes would seem to be intermediate between atoms & chromosomes. I see usage of the term genetic material within a DNA molecule, but is it too early yet to say that genes can be identified as being particular pieces or strands on DNA molecules (as a string of atoms)?--JimWae 04:25, 2005 Mar 27 (UTC)

It goes without saying that life breaks boundaries and defies its own conventions all the time. So our shorthand definitions, our abstractions, are going to be wrong sometimes. I don't think hard-and-fast definitions are that important, really, just delivering the broad strokes. That's pretty much how biology works - learn the broad strokes, and fill in lots and lots of nuance. We can work on filling in some of the nuance - e.g. the original query highlights the fact that RNA genes are ignored by the given definition. Graft 04:45, 27 Mar 2005 (UTC)

I noticed some bias on the table on genes. It shows humans having the most genes and most base pairs among all the examples given. One could conclude that we are the most "advanced" specie, or that the number of genes is a sign of intelligence maturity, name it.. I'm no specialist in this field but I recall reading that there are organisms that have a higher number of genes than humans... I think that would be a good addition to the table to dismiss the notion that humans ar at the top of the scale.... 08:46, 5 Oct 2004 (UTC)

[edit] Overhaul table of gene number and genome size?

I think the table listing the gene count of different organisms is slightly misleading, and overly simplistic. Categories such as 'Plants' or 'Flies' are too wide. I think the range of genome size and gene count in plants will be substantial. Maybe the table should only show examples from specific species and actually list the species name to avoid further confusion. E.g.

Arabidopsis thaliana (thale cress) 120 Mb ~25,000 Saccharoymces cerevisiae (yeast) 14 Mb, ~6,000 Drosophila melanogaster (fruit fly) .... etc.

I don't mind doing this if there are no objections.

Keith

Also, could someone explain what the significance of the genome size actually is? It seems surprising that rice (decoded today with about 37,500 genes, see [1]) has more genes than humans (25,000). Why is this? Are human genes longer? Are plants more complicated than humans? Are there lots of dormant genes in plants?

• I believe it is because plants are more complicated: not only do they do cell growth, cell division, cellular respiration in a manner similar to other organisms (animals, fungi), but they also do photosynthesis. They must take in raw materials -- ammonia or nitrate, phosphorus, etc, and construct all sugars, amino acids, and nucleotides from scratch. Heterotrophs can absorb pre-constructed molecules. Furthermore, they have a complex 'secondary metabolism' that varies among taxa and is involved in defense against herbivores and pathogens, and other aspects of their ecology. It's tough being a plant! Satyrium 19:12, 18 August 2006 (UTC)

[edit] kudos

A year or two ago I was active in this article and involved in various edit wars. Today is the first time I have read over it in a long, long, time -- and I want to congratulate all the people who have been working on it. While I am sure it can still be improved, I think you have really turned out a well-written, clear, comprehensive article. It restores my faith in Wikipedia, Slrubenstein 21:51, 7 Dec 2004 (UTC)

Regarding the Dawkins - I haven't read him, but characterizations of his description seem far too anthropomorphic. That is, DNA does not exist to selfishly propagate itself. DNA is a stupid molecule that, left to itself, would slowly degenerate into nucleic acids. But genes that are good at propagating themselves, even at the expense of their organism, will thrive and become prevalent. This isn't as succinct an idea as the "selfish gene" sentence, but it is more accurate. The question is, is this Dawkins' charcterization? Graft 23:00, 7 Dec 2004 (UTC)

Well, I am pretty sure you are referring to the text that was there before I made my additions. I too have problems with the anthropomorphizing, but my sense is, it is in Dawkins (and anthropologists and other social critics who object to this aspect of Dawkins' work usually use this as a jumping off point, that this kind of sociobiology is just the theory of evolution refracted through contemporary bourgeoise ideology). Note there is a problem even in your phrasing, "genes that are good at propegating themselves" because of course it is not the gene that propegates itself but the organism, which involves that gene and many more and environmental and random factors. In any event, IF you want to keep in the Dawkins paragraph, the task is to represent hs views accurately, not to represent our own views. I myself am pretty critical of him, I just wanted his view to be presented more fairly. Slrubenstein

How ironic... hard to escape the urge to attribute intent to everything, I guess. Um, but, okay, this is all I wanted to clarify: that Dawkins actually does anthropomorphize that way. Graft 21:07, 8 Dec 2004 (UTC)

It's been many years since I read The Selfish Gene, but I don't recall that Dawkins was particularly anthropomophic in his descriptions; not more than most biologists who talk about the "purpose" of some aspect of biology. I've rewritten that section to better conform to my memory. I'll try to double check a copy of the text. --Rikurzhen 22:03, Dec 8, 2004 (UTC)

The very word "selfish" anthropomorphizes. Slrubenstein | Talk 20:09, 27 Mar 2005 (UTC)

"anthropomorphizes" isn't quite accurate, since non-human animals could righly be said to be selfish. Dawkins could be charged with the pathetic fallacy, but from my reading of The Selfish Gene, the term selfish isn't meant literally, but rather just to describe--by analogy to an easy to understand term--the equilibrium outcome of gene evolution. --Rikurzhen 22:29, Mar 27, 2005 (UTC)

Isn't it awesome how time has almost no meaning on Wikipedia? 06:01, 28 Mar 2005 (UTC)

[edit] Request for references

Hi, I am working to encourage implementation of the goals of the Wikipedia:Verifiability policy. Part of that is to make sure articles cite their sources. This is particularly important for featured articles, since they are a prominent part of Wikipedia. The Fact and Reference Check Project has more information. Thank you, and please leave me a message when you have added a few references to the article. - Taxman 18:55, Apr 21, 2005 (UTC)

[edit] Sentence moved here from article.

"Some people say the "got lost in the gene pool" to say they are ugly."

This sentence was a sore thumb where I found it in this article. Feel free to add it elsewhere in the article. P.MacUidhir (t) (c) 16:19, 15 November 2005 (UTC)

Dude, it is a sore thumb even on the talk page. Slrubenstein | [[User talk:Slrubenstein|Talk]] 18:48, 15 November 2005 (UTC)

[edit] new models of evolution and genes - call for experts out there to address an issue

While the paragraph on Dawkins is important, I think by itself it carries too much weight in the article. I am not an evolutionary biologist, but I know that among evolutionary biologists there is much talk of a new model of evolution that takes into account the fact that all organisms share a great deal of genetic material, that what makes (literally) one organism different from another — just like the process that makes one organ different from another (in the same organism) — is not that they have different genes for a given trait, but rather that they have or lack genes that switch on the gene for a given trait (in other words, the cells in my hand and liver contain the same genes, but in the process of embryonic development "hand" genes switched on in some cells but not others, while "liver" genes switched on in some cells but not others. Similarly, humans have genest that play a role in the embryonic development of dogs, but that just never get switched on in humans; conversley, dogs have genes that play a role in the embryonic development of humans, but they just never get switched on in dogs). This model has significant implications for the theory of evolution, because natural selection would not be acting on the genes for given organs (e.g. gills or lungs, wings or arms) but rather the genes that function as switches. This is a different model than Dawkins. I know full well that this model is not universally embraced by evolutionary biologists, and that even among those who embrace it, there are differences in the importance they claim for our understanding of speciation. Nevertheless, I do know that these are things evolutionary biologists are discussing, and I think it should be reflected in the article. Since I do not know any of the scholarly literature on this, I am not competent to provide an accurate NPOV account of it in the article. But is there anyone out there who knows what I am referring to, knows it well enough to see where I am misinterpreting or misunderstanding it, and knows it well enough to add a section to the article that makes its significance, or potential significance, clear? Slrubenstein | [[User talk:Slrubenstein|Talk]] 19:06, 15 November 2005 (UTC)

You're getting at a subject of study at the interface of developmental and evolutionary biology sometimes called evo-devo. (You may be mixing that up a bit with the matter of inclusive fitness, which is linked closely with the gene-centered view of evolution.) Evo-devo is AFAIK at a different level than the question of whether evolution operates from a gene-centric view. But yeah, there's tons of stuff that could be added to this article. --Rikurzhen 19:33, 15 November 2005 (UTC)

Yes, evo-devo, that is what I meant to say. I am not rejecting the principle of inclusive fitness, but as an outsider it does seem to me that evo-devo has implications concerning the gene-centered view of evolution. Clearly you know far more than I do, I hope at some point you will find the time to put some of it in, to the appropriate articles. Slrubenstein | [[User talk:Slrubenstein|Talk]] 21:09, 15 November 2005 (UTC)

There very well could be a connection. I just don't know of one -- but my lack of familariity is not an indication that no one was written about it. However, inclusive fitness has implications even for single celled organisms, whereas evo devo is mostly about animals. --Rikurzhen 22:39, 15 November 2005 (UTC)

There's two things at work here: one is that the idea of "genes as the unit of selection" is obviously too simplistic, and now that molecular biology and genomics allows us to chase function down to the individual base-pair level, we don't need to restrict ourself to thinking in terms of gross elements like whole genes. The other is the fact that functional divergence in genes doesn't seem to meet up with the picture set by organismal complexity (e.g. human and C. elegans have a similar number of genes); also, divergence of form by contemporary accounts has a lot more to do with differences in gene expression (e.g. the faddish "Hox" genes) than changes in genes themselves. Thus the desire to chase evolution into regulatory regions. Since that's relatively unknown territory, it'll probably be a while before we can know whether this is a reasonable line of argument. Graft 18:13, 16 November 2005 (UTC)

[edit] Cistron currently redirects here ...

Cistron currently redirects to this article, but the current article content does not support that redirection. Is there a more appropriate article that addresses prokaryotic genes to which "cistron" could be re-targeted? User:Ceyockey (talk to me) 16:10, 15 January 2006 (UTC)

[edit] Typical numbers of genes in an organism: Differentiate for plants

The number of genes in plants vary hugely, so we should probably differentiate that part. I seem to recall that Arabidopsis thaliana and some Pinus species are at the extremes of the known distribution... - Samsara _contrib ^talk 22:18, 25 January 2006 (UTC)

Plants have several times undergone genome duplication events (and some have done so recently without changing much), so it's not unusual for them to have ridiculous chromosome numbers and correspondingly large genomes... Graft 00:26, 26 January 2006 (UTC)

I'm aware of that. Although your post is not directly countering my suggestion, I might point out that many (most?) genes have arisen by duplication. - Samsara _contrib ^talk 00:52, 26 January 2006 (UTC)

Yeah, but gene duplication is not the same as genome duplication. I'm merely suggesting that a huge number for plant genome size is probably representative. Graft 17:45, 26 January 2006 (UTC)

gene duplication is not the same as genome duplication

True, though both have the potential to lead to divergent gene function. I don't know what the wikipedia consensus is for what constitutes a plant (no time to read the article just now), but we have to be careful not to think only of angiosperms. - Samsara _contrib ^talk 20:49, 26 January 2006 (UTC)

[edit] Human genome is Science Collaboration of the Week

Just to let you know that Human genome has been voted Science Collaboration of the Week. - Samsara _contrib ^talk 10:32, 27 January 2006 (UTC)

[edit] WP:FARC

I hate to do this but I'm going to list this article on FARC - it simply does not deserve to be featured in my opinion. Why?

1. Lacks inline citations
2. the lead is too long & does not conform to WP:LEAD
3. neither "History" nor "Evolutionary concept of gene" are comprehensive.

As a courtesy, I'll give the contributors to this article some time to address these concerns before I take it to FARC. Mikker ^... 17:20, 11 February 2006 (UTC)

I've now listed the article at FARC. Mikker ^... 21:02, 12 February 2006 (UTC)

[edit] What are Thrifty Genes?

I've heard the term used a couple times, but since it's being used to advertise a dieting concept I'm not sure how verifiable it is. It does quote a journal though, is it a good journal? Here's the quote:

Journal of Applied Physiology 96:3-10, 2004

“Survival of Homo sapiens during evolution was dependant on the procurement of food…

To ensure survival during periods of famine, certain genes evolved to regulate efficient intake and utilization of fuel stores. Such genes were termed “Thrifty Genes” in 1962. Farther more, convincing evidence shows that this ancient genome has remained essentially unchanged over the past 10,000 years and certainly not changed in the past 40-100 years.

Although the absolute calorie intake of modern day humans is likely lower compared with our hunter-gatherer ancestors, it is nevertheless in positive calorie balance in the majority of the US adult population. We contend that the combination of continuous food abundance and physical inactivity eliminate the evolutionary programmed biochemical cycles emanating from feast-famine and physical activity-rest cycles, which in turn abrogated the cycling of certain metabolic processes, ultimately resulting in metabolic derangements such as obesity and type2 diabetes.”

“Manu V. Chakravarthy 1 and Frank W. Booth 2

1Division of Endocrinology, Metabolism and Lipid Research, Department of Internal Medicine, Washington University School of Medicine, St. Louis 63110; and 2Departments of Biomedical Sciences and of Medical Pharmacology and Physiology and the Dalton Cardiovascular Institute, University of Missouri, Columbia, Missouri 65211”

Now obviously such concepts have to do with how genes are activated and deactivated. My knowledgee is limited, but it's endocrinology, hormones and steroids that control that kind of thing, right? As diet may influence those, I wonder if there may indeed be adaptory aspects. Whether or not it's proven though, is confusing. So, can anyone help in forming the beginnings of an article on this, linked to in this page and possibly others such as diabetes and fat loss? --Tyciol 09:38, 14 February 2006 (UTC)

[edit] Modifier gene

... missing. --129.11.76.216 14:30, 13 March 2006 (UTC)

... inscrutable. Graft 20:28, 13 March 2006 (UTC)

Not a real phenomenon, only a mathematical tool. Samsara (talk • contribs) 18:41, 5 December 2006 (UTC)

[edit] 0.5 version nomination

Failed on quality: (Not a FA, as stated) failed for same reason it was at FARC. Chuck^(척뉴넘) 01:47, 29 May 2006 (UTC)

Why? If you tell me your problems about the article, I'll work on it. I find it important to put Gene into V0.5. NCurse _work 10:33, 29 May 2006 (UTC)

[edit] Usually?

The article reads ". . .encoded in the organism's genetic material (usually DNA or RNA). . ."

usually? Is there an exception to DNA or RNA?

It depends on the organism. We know RNA-based viruses. NCurse _work 13:49, 23 August 2006 (UTC)

[edit] embryology

Does anyone happen to know any embryologists? I think Embryology really needs a lot of expert attention. would sympathtic editors consider a positive vote here? [2]Slrubenstein | Talk 16:56, 28 August 2006 (UTC)

I take a look, thanks, but maybe you should search for experts here: Wikipedia:WikiProject Expert Request Sorting or have a look at that: Category:Pages needing expert attention. NCurse _work 20:06, 28 August 2006 (UTC)

Thanks! Slrubenstein | Talk 20:43, 28 August 2006 (UTC)

[edit] Organization of this article

The way the content in this article is organized makes my brain ache. I propose this structure, or something like it (roughly following Watson et al. Molecular Biology of the Gene, but moving expression above maintenance/DNA repair):

• Classical genetics and Mendelian inheritance (BRIEF; this already has its own article - a paragraph or two)
• The physical gene: DNA and RNA

• Promoters, repressors, and enhancers
• Introns and exons
• Differences between eukaryotic and prokaryotic genes, including operons

• Gene expression

• The genetic code, Transcription, Translation (Brief, covered elsewhere)
• Gene regulation
• Functional RNA

• Genes and inheritance

• Relationship to classical heredity

• Evolution of genes

• Mutation and repair
• Exon shuffing
• Pseudogenes

• Genes in genomes (Brief, covered elsewhere)
• Human genetic disorders (Brief, covered elsewhere)

Thoughts? I wonder about leaving the 'genome' section so far down, but this organization has the advantage of presenting the familiar classical context and thereafter following a small-to-large progression from focus on a single gene to focus on the whole genome. I also thought about giving 'mutation' its own top-level section before 'gene expression'. Opabinia regalis 06:07, 5 December 2006 (UTC)

It is a mess now I agree. It needs reworking so much I wouldn't want to discourage anyone with dispute, but I don't see anything wrong with your plan :) I like mutation being in replication, or at least after it if there is too much mutation material. - cohesion 07:01, 5 December 2006 (UTC)

Great idea. What about mess DNA? NCurse _work 18:36, 5 December 2006 (UTC)

Sorry, do you mean 'junk DNA'? Maybe there should also be a 'genomic organization' section that covers 'junk'/noncoding DNA, telomeres, etc, or is that too far outside the scope of this article? Opabinia regalis 03:11, 10 December 2006 (UTC)

We need to focus this article more on the subject of genes. Tried to edit the above list to reflect this. TimVickers 21:15, 9 January 2007 (UTC)

Largely agree, though I think there ought to be at least some explanation of the connection between classical and molecular inheritance, which necessitates some dicussion of the cell cycle. Other than that I'm happy to defer to your judgment on the matter, since you have much better intuition about writing articles for general audiences that are still complete and precise. I've been hoping someone would wander into this article since I nominated it for SCOTM, but unfortunately nothing much has changed yet. Opabinia regalis 02:33, 10 January 2007 (UTC)

[edit] Effluvia

After a recent rewrite (which surely needs editing for completeness and accessibility), I removed these two sections from the article, which I considered rather poorly written. I'm dumping them here for easier reference than in the history, because some of this material - the subjects, if not this exact text - should make it back into the article eventually. Opabinia regalis 06:06, 10 December 2006 (UTC)

---

Many steps lie between the gene and its effect

For various reasons, the relationship between DNA strand and a phenotype trait is not direct. The same DNA strand in two different individuals may result in different traits because of the effect of other DNA strands or the environment.

• The DNA strand is expressed into a trait only if it is transcribed to RNA. Because the transcription starts from a specific base-pair sequence (a promoter) and stops at another (a terminator), our DNA strand needs to be correctly placed between the two. If not, it is considered as junk DNA, and is not expressed.

• cells regulate the activity of genes in part by increasing or decreasing their rate of transcription. Over the short term, this regulation occurs through the binding or unbinding of proteins, known as transcription factors, to specific non-coding DNA sequences called regulatory elements. Therefore, to be expressed, our DNA strand needs to be properly regulated by other DNA strands.

• The DNA strand may also be silenced through DNA methylation or by chemical changes to the protein components of chromosomes (see histone). This is a permanent form of regulation of the transcription.

• The RNA is often edited before its translation into a protein. Eukaryotic cells splice the transcripts of a gene, by keeping the exons and removing the introns. Therefore, the DNA strand needs to be in an exon to be expressed. Because of the complexity of the splicing process, one transcribed RNA may be spliced in alternate ways to produce not one but a variety of proteins (alternative splicing) from one pre-mRNA. Prokaryotes produce a similar effect by shifting reading frames during translation.

• The translation of RNA into a protein also starts with a specific start and stop sequence.

• Once produced, the protein interacts with the many other proteins in the cell, according to the cell metabolism. This interaction finally produces the trait.

---

Modern concepts of the gene

When trying to understand the concept of a gene, keep in mind that it is not static. It has evolved considerably from a scarcely explained "unit of inheritance" without a physical basis (see history section) to a usually DNA-based unit that can exert its effects on the organism through RNA or protein products. It was also previously believed that one gene makes one protein. This concept has been overthrown by the discovery of alternative splicing.

And the definition of gene is still changing. The first cases of RNA-based inheritance have been discovered in mammals.^[1] In plants, cases of traits reappearing after several generation of absence have lead researchers to hypothesise RNA-directed overwriting of genomic DNA.^[2] Evidence is also accumulating that the control regions of a gene do not necessarily have to be close to the coding sequence on the linear molecule or even on the same chromosome. Spilianakis and colleagues discovered that the promoter region of the IFN-γ gene on chromosome 10 and the regulatory regions of the T(H)2 cytokine locus on chromosome 11 come into close proximity in the nucleus maybe to co-regulate.^[3]

The concept that genes are clearly limited is also being eroded. There is evidence for fused proteins stemming from two adjacent genes that can produce two separate protein products. While it is not clear whether these fusion proteins are functional, the phenomena is more frequent than previously thought.^[4] Even more ground-breaking than the discovery of fused genes is the observation that some proteins can be composed of exons from far away regions and even different chromosomes.^[5]

[edit] Referencing elementary material

Much of the content in this article will be uncontroversial, basic, standard textbook material, and Wikipedia:Scientific citation guidelines is seemingly in limbo. Not that it shouldn't also cover current research, but for accessibility and brevity, it should stick mostly to the well-established facts. This is something I always find annoying and difficult to do well - does anyone have ideas on how to provide 'sufficient' inline citations for masses of basic material without breaking up the text with repeated footnotes to the same source? Opabinia regalis 07:07, 10 December 2006 (UTC)

My suggestion here is that gene or genetics attempt to do the same as we have done for evolution and has been done for special relativity and general relativity. That is, an Introduction to Genetics article be created in Wikipedia to allow easier access to the material. I would be glad to help. I propose to use the Simple Wikipedia article as a basis, and then we can edit it to be more suitable, just as was done in the case of Introduction to evolution. --20:14, 12 December 2006 (UTC)

[edit] Lead section comments

As an outsider, I thought I would offer a comment or two on your lead section and my impressions:

A gene is the unit of heredity in every living organism.

• a bit difficult for me to understand. What is a "unit" of heredity? I am not sure about the first sentence.

Genes are encoded nucleic acid molecules known as DNA or RNA, and direct the physical development and behavior of the organism.

• the average person will have heard of DNA, but probably not RNA. The average person will not know what a nucleic acid is, and should not be required to look too much up in the first paragraph! Even if there is a wikilink, it is best to make it self contained for the reader. Also using the word encode is not very good for the general audience.

Most genes encode proteins, which are biological macromolecules comprising linear chains of amino acids that affect most of the chemical reactions carried out by the cell.

• The average person has heard the word protein, but does not know what it is aside from something we eat. Some will not know the word linear. People will know molecule maybe, but not macromolecule. Amino acid again is unfamiliar. A cell might be known as a small part of a plant or animal, but even chemical reactions might be poorly understood.

Some genes do not encode proteins, but produce non-coding RNA molecules that play key roles in protein biosynthesis and gene regulation.

• Getting too dense. Encode? How do they encode proteins? What is noncoding? What is protein biosynthesis? Gene regulation? You are requiring the reader to look too much up. They will give up.

Molecules that result from gene expression, whether RNA or protein, are collectively known as gene products.

• Gene expression ? what is that? A guy named Gene who smiles?

Most genes contain non-coding regions, that do not code for the gene products, but often regulate gene expression.

• round and round the mulberry bush

A critical non-coding region is the promoter, a short DNA sequence that is required for initiation of gene expression.

• the promoter? Like a circus barker?

The genes of eukaryotic organisms often contain non-coding regions called introns which are removed from the messenger RNA in a process known as splicing.

• blah blah blah. Just sounds like noise to the average person.

The regions that actually encode the gene product, which can be much smaller than the introns, are known as exons.

• The exon. Like the Exon Valdise? The text in the figure also is too dense. I think that text should stand on its own and tell a story without much need to follow links.

The total complement of genes in an organism or cell is known as its genome.

• Maybe understandable. But maybe not. Complement is a big word and might be misunderstood.

The genome size of an organism is loosely dependent on its complexity; prokaryotes such as bacteria and archaea have generally smaller genomes, both in number of base pairs and number of genes, than even single-celled eukaryotes.

• Compound sentences are never good. And the words are too big.

However, the largest known genome belongs to the single-celled amoeba Amoeba duria, with over 6 billion base pairs.^[6] The estimated number of genes in the human genome has been repeatedly revised downward since the completion of the Human Genome Project; current estimates place the human genome at just under 3 billion base pairs and about 20,000-25,000 genes.^[7]

• People do not know what a base pair is or what this means.

The gene density of a genome is a measure of the number of genes per million base pairs (called a megabase, Mb); prokaryotic genomes have much higher gene densities than eukaryotes due to the absence of introns in prokaryotic genomes.

• compound sentence. Bi words.

The gene density of the human genome is roughly 12-15 genes/Mb.^[8]

• meaningless. Certainly for the introduction.

So take a look at these comments, and maybe consider some rewriting.--Filll 13:26, 13 December 2006 (UTC)

Sorry Filll, I totally missed this post. The lead hasn't changed much (except for a paragraph on human genome stuff) from its former lame state; I was going to get back to it after the text was in better shape. Thanks for the comments; I'll rewrite this sometime after the holidays. Opabinia regalis 04:41, 23 December 2006 (UTC)

[edit] old table

Replacing the table with a cited version, which is slightly out of date but from a solid source (Molecular Biology of the Gene). Reproducing the old table here for reference. Opabinia regalis 03:08, 21 December 2006 (UTC)

Gene content and genome size of various organisms

organism	genes	base pairs
Plant	<50,000	<1011
Human, mouse or rat	25,000	3×109
Fugu fish	40,000	4x108
Fruit Fly	13,767	1.3×108
Worm	19,000	9.7×107
Fungus	6,000	1.3×107
Bacterium	500–6,000	5×105–107
Mycoplasma genitalium	500	580,000
DNA virus	10–900	5,000–800,000
RNA virus	1–25	1,000–23,000
Viroid	0–1	~500

[edit] Trichomonas vaginalis

26k genes for a protozoa. Quite impressive... [3]. Someone else can add it Nil Einne 16:55, 12 January 2007 (UTC)

[edit] Lead Problem

"Here's the first line of the Wikipedia entry for 'gene':

gene is the unit of heredity, with each gene determining one inherited feature of an organism.'

is completely wrong. 'One gene, one character' is a false idea of the relationship of genes to inheritance, since many genes contribute to the appearance of a single feature, and one gene will play a role in many different features."

Oh, dear... Adam Cuerden ^talk 19:58, 16 January 2007 (UTC)

The offending sentence is mine. The problem is that a gene is an extremely difficult thing to define, even using technical terms. Do they include promoters? Regulatory elements? What about rRNA genes, or siRNA genes? I've tried again with a transcript-based definition. TimVickers 20:17, 16 January 2007 (UTC)

Each gene encodes for one or more proteins, or other regulatory elements? Have to remember alternate splicing of introns, though that's a truncation event, in effect, it still counts as multiple proteins. Adam Cuerden ^talk 20:39, 16 January 2007 (UTC)

With rRNA, snoRNA and siRNA we can't define genes in terms of proteins any more. I think one gene - one transcript is usually true, although alternate start sites cause problems with that generalization. TimVickers 21:33, 16 January 2007 (UTC)

Not really. I do remember several proteins that have various truncated forms, caused by alternate splicings. It's common enough that we need to mention it. Anyway, a lot of the introns have regulatory functions. Adam Cuerden ^talk 21:51, 16 January 2007 (UTC)

Multiple splice forms all come from post-transcriptional processing of a single transcript. It's not true that one gene = one mRNA, but in general one gene = one transcript. TimVickers 22:05, 16 January 2007 (UTC)

Point, that. Probably implied already, though. Oh, and you know that Dawkins uses a completely different definition of gene again in The Selfish Gene? Just to make it awkward? Basically, anything that tends to be inherited together, no matter how many transcripts. Adam Cuerden ^talk 22:15, 16 January 2007 (UTC)